The goal of this proposal is to understand the mechanisms by which angiogenesis (new blood vessel growth) is regulated by a protein receptor called CD36 that is expressed on the surface of microvascular endothelial cells. These are the cells that form the lining of blood capillaries. Angiogenesis is a critically important process in the development of many human diseases, including heart attack stroke, diabetes and cancer. Therefore, understanding how the body normally turns angiogenesis on and off has direct potential to lead to new therapeutic and prognostic approaches to many diseases. CD36 functions by sending a signal to microvascular endothelial cells to halt angiogensesis when it is exposed to any of a group of other proteins that contain a structural domain called the thrombospondin type I repeat (TSR). Our laboratory has recently disovered that a protein circulating in blood, called HRGP, bears structural similarity to CD36 and can act as a "decoy", blocking the activity of TSR-containing anti-angiogenic proteins. These discoveries have led to the hypothesis that angiogenesis is modulated by the fine control of CD36, TSR and HRGP expression in tissues. To address the hypothesis three specific aims have been developed. The first is to identify the structural determinants involved in recognition of TSR domains by CD36 and to characterize modulation of TSR binding by oxidized phospholipids. The approach will involve generating recombinant peptides, studying their interaction, and using NMR spectroscopy to define the mechanisms of the interactions at the atomic level. Aim 2 will characterize expression of CD36 in human microvascular endothelial cells, focusing on the mechanisms by which CD36 expression or function is down-regulated by modified phospholipids via protein kinase C activation and by ecto-domain phosphorylation. Expression will be measured at the mRNA and protein levels. The biological importance of these regulatory pathways in vivo will be determined in aim 3, in which angiogenesis associated with UVB skin radiation and tumor growth will be studied in mice with targeted deletion of the cd36 and hrgp genes and transgenic mice that over-express HRGP in skin. Accomplishing these aims could lead to new therapeutic approaches to modulate angiogenesis through the CD36-mediated anti-angiogenic switch. PUBLIC HEALTH RELEVANCE: Angiogenesis (new blood vessel growth) is a critically important process in the development of many human diseases, including heart attack, stroke, diabetic retinopathy, and cancer. Therefore, understanding how the body normally turns angiogenesis on and off has direct potential to lead to new therapeutic and prognostic approaches to many diseases. This project seeks to understand the cellular mechanisms by which an anti-angiogenic switch on blood vessel lining cells (endothelial cells) is turned on and off. The switch is mediated by a cellular receptor called CD36 which functions by sending a signal to endothelial cells to halt angiogenesis when it is exposed to any of a group of other proteins that contain a structural domain called the thrombospondin type I repeat (TSR). This project will define the structural basis of TSR- CD36 interactions, determine how expression of the key components of the system are regulated, and determine the functional role of the system in regulating angiogenesis during inflammation and tumor growth in vivo.